This invention relates to detergents for dishwashing machines (dishwasher detergents) which contain polymers bearing sulfonic acid groups and, in addition, have another beneficial effect. The polymers containing sulfonic acid groups are copolymers of i) unsaturated carboxylic acids, ii) monomers containing sulfonic acid groups and iii) optionally other ionic or nonionic monomers. The detergents may be formulated as solids or liquids, for example as powders, granules, extrudates, tablets, liquids or gels.
Today, machine-washed tableware has to meet stricter requirements than hand-washed tableware. Thus, even tableware completely free from food residues is regarded as unsatisfactory when, after dishwashing, it still has whitish stains which are attributable to water hardness or other mineral salts and which come from water droplets that have remained on the tableware through lack of wetting agent and dried.
Accordingly, to obtain bright, spotless tableware, rinse agents are now successfully used. The addition of rinse agent at the end of the wash program ensures that the water drains completely from the tableware so that the various surfaces are bright and free from residues at the end of the dishwashing program.
The cleaning of tableware in domestic dishwashing machines normally comprises a prerinse cycle, a main wash cycle and a final rinse cycle which are interrupted by intermediate rinse cycles. With most machines, the prerinse cycle can be selected for heavily soiled tableware, but is only selected by the consumer in exceptional cases so that, in most machines, a main wash cycle, an intermediate rinse cycle with clean water and a final rinse cycle are carried out. The temperature of the main wash cycle varies between 40 and 65° C., according to the type of machine and the program selected. In the final rinse cycle, rinse aids which normally contain nonionic surfactants as their main constituent are added from a dosing tank. These rinse aids are liquids and are widely described in the prior art. Their principal function is to prevent lime stains and bloom on the cleaned tableware. Besides water and low-foaming nonionic surfactants, many rinse aids often contain hydrotropes, pH regulators, such as citric acid, or bloom-inhibiting polymers.
EP-B1 0 197 434 (Henkel) describes liquid rinse agents which contain mixed ethers as nonionic surfactants. A wide variety of materials (glass, metal, silver, plastic, china) is cleaned in dishwashers. These various materials have to be thoroughly wetted in the final rinse cycle. Rinse agent formulations containing only mixed ethers as their surfactant component satisfy these requirements inadequately, if at all, so that the clear rinse effect or drying effect is unsatisfactory, particularly on plastic surfaces.
The storage tank in the dishwashing machine has to be filled with rinse agent at regular intervals, one filling being enough for 10 to 50 rinse cycles according to the type of machine. If the consumer forgets to fill the tank, glasses in particular are spoiled by lime stains and bloom. Accordingly, some proposals have been put forward in the prior art with a view to integrating a rinse agent in dishwasher detergents. These proposed solutions are confined to tablets.
Thus, European patent application EP-A-0 851 024 (Unilever) describes two-layer detergent tablets of which the first layer contains peroxy bleaching agent, builder and enzyme while the second layer contains an acidifying agent, a continuous medium with a melting point of 55 to 70° C. and bloom inhibitors. The high-melting continuous medium is said to release the acid(s) and bloom inhibitor(s) with delay and to develop a clear rinse effect. Powder-form dishwasher detergents or surfactant-containing rinse agent systems are not mentioned in this document.
The problem addressed by the present invention was to provide new dishwasher detergents which would at least match commercially available detergents in their performance properties and which, in addition, would afford other performance-related advantages. The new detergents would be usable both as conventional detergents and in the form of combination products and would develop their favorable properties irrespective of their supply form.
It has now been found that the use of polymers containing sulfonic acid groups in dishwasher detergents has advantageous effects if, in addition to the polymers containing sulfonic acid groups, the detergents contain large quantities of nonionic surfactants. With detergents according to the invention of this embodiment, the quantities of surfactant remaining in the machine after the main wash cycle and the intermediate rinses provide for adequate drainage behavior in the final rinse cycle so that the water running off the tableware does not leave any stains behind on drying. Where these detergents according to the invention are used, the final rinse cycle does not have to be charged with additional, intentionally added rinse agents.